1. Field of the Invention
This invention relates generally to a method of configuring satellite constellation designs using multiple discrete switchable beams. Further, the present invention relates to a method of configuring antenna feeds in a feed array of an antenna in a satellite and the positioning of the satellite in orbit to maximize coverage for profitability, flexibility, changing demand, and redundancy for a satellite network.
2. Discussion of the Related Art
Today the skies above us have become crowded with communication satellites whose sole function is to relay information received from ground stations to other ground stations. The types of satellites utilized for communication generally fall into two categories based on the satellites"" position above the planet. The first type is low Earth orbiting satellites, while the second are in a geo-synchronous Earth orbit. In the case of geo-synchronous Earth orbiting satellites, the satellite remains in the same relative position above the earth, and a parabolic satellite dish is typically used to send and receive signals to and from the satellite. In the early days of satellite communication, these geo-synchronous orbiting satellites were confined to telephone communications. However, today all forms of information are being relayed by these geo-synchronous satellites including, but not limited to, voice, computer data, video, television, radio and satellite telephones.
Therefore, today several major industries are heavily dependent upon reliable communications service via satellites being continuously available. Unfortunately, satellites fail, just as all electronic equipment made by man eventually must be repaired or replaced. However, it is at present impossible to send a repairman immediately to repair a satellite in geo-synchronous orbit. In the early days when satellites were used exclusively for telephone communications, landlines and undersea cables still could be used to provide access for customers if a satellite failed. However, this is no longer the case for other applications for which communications satellites in geo-synchronous orbit are used for.
FIG. 1 is an illustration of a satellite communication network configuration in which total redundancy is provided by two satellites. Satellites 20 and 40 are used to communicate to ground stations 30 located within a region of the planet Earth 10 using a uniform distribution methodology. This uniform distribution methodology would allow for communications to an entire region of Earth 10, such as, but not limited to, North America. Should either satellite 20 or satellite 40 fail, the other satellite may completely take over its communications function. However, this complete redundancy solution is expensive to implement since two satellites must be used just in case one fails. Further, should demand increase in one location it may not be possible to reconfigure the satellites in orbit to handle the additional load from the increased traffic seen in one area. In addition, building in excess capacity in a satellite may not be possible at the time the satellite is being designed, since that may be more than a year in advance of it being launched.
FIG. 2 is an example illustration of the coverage that may be seen from three satellites using the uniform distribution methodology. Coverage areas 200 and 210 may be generated by satellites 20 and 40 in which, rather than complete overlap and redundancy, only partial overlap in a geographical area is accomplished. Via this mechanism satellite 20 would provide coverage area 200 and satellite 40 would provide coverage area 210. Overlap would occur in such areas as the East Coast of United States, Central America, and portions of South America. Therefore, should satellite 20 fail, the East Coast of United States could still be covered through satellite 40. However, this still leaves the West Coast of United States without service, and should traffic increase in demand in the Midwest, such as Chicago, even with both satellites 20 and 40 in full operation, inadequate service could potentially be seen via communications through satellite 20.
One mechanism utilized to overcome the foregoing problems of redundancy and capacity has been to utilize multiple feeds to form multiple spot beams to target specific locations on the planet Earth 10. However, the performance degradations of spot beams over a wide geographic region have previously limited the spot beam applications to a relatively small number of feeds within a single antenna. However, as illustrated in U.S. Pat. No. 6,211,835 to Pebbles et al., U.S. Pat. No. 6,236,375 to Chandler et al., and U.S. Pat. No. 6,215,452 to Chandler et al., herein incorporated by reference in their entireties, it is now possible to have a large number of spot beams in which each spot beam individually targets specific locations on the planet Earth 10 using what is hereinafter referred to as a hemispherical earth coverage antenna.
FIG. 3 is an illustration of spot beams positioned over predefined Earth locations utilizing the previously mentioned hemispherical earth coverage antenna. Three different satellites 300, 310, 320 are shown respectively located at 101 degrees west longitude, 47 degrees west longitude, and 122.5 degrees east longitude. The satellite 300 has most of its spot beams 330 directed towards the North American continent. Satellite 310 positions its spot beams 340 to cover South America and the East Coast of The United States. Satellite 320 in turn has its spot beams 350 distributed to cover portions of Asia and Australia. It should be noted that more than one spot beam may be directed at any given location within the range of the satellite. Further, the positioning of the spot beams is dependent upon the physical alignment of the feeds in the antenna of the satellite and the longitude at which the satellite is positioned in geo-synchronous orbit, as detailed in U.S. Pat. Nos. 6,211,835, 6,236,375, and 6,215,452, incorporated herein by reference in their entireties. Once the feeds are set within a satellite, they may not be changed individually to target another geographical location. However, unlike a uniform distribution method, using this non-uniform methodology the spot beams may be directed towards those areas where demand is highest and profitability maximized. Therefore, the positioning of feeds to generate spot beams is critical in determining the profitability and redundancy of a satellite communications network.
However, a tool such as a hemispherical earth coverage antenna, without a comprehensive method of configuring the feeds and positioning the satellites, is like having all the materials to build a house without the blueprints. Even an experienced contractor might discover needlessly duplicated work or work items completely left off the structure. In the case of a global satellite communications system in geo-synchronous Earth orbit, several factors must be taken into consideration in the configuring of feeds on individual antennas and the positioning of satellites in geo-synchronous orbits to maximize profitability, coverage and redundancy in case of failure of a satellite. These factors include present demand for satellite communications, population shifts which may impact future demand, areas which may be prone to sudden shifts in demand, areas where constant uninterrupted service is absolutely necessary. Predicting such factors in order to properly configure a satellite and place it in the proper orbit is difficult, to say the least. Further, unforeseen circumstances may require thereplacement, substitution or reconfiguration of a satellite, which may be extremely difficult to do while the satellite is being built.
Therefore, what is needed is a system, method and computer program that will enable spot beam coverage of identified high traffic/profit geographical locations such as cities. Further, this system, method and computer program should allow for the switching of spot beams to concentrate capacity on a particular geographic area when unexpected high demand is seen in that area. Further, this system, method and computer program should further build in redundancy in the positioning of spot beams and satellites so that when a failure occurs in a satellite, other antennas on that satellite or other satellites in orbit may immediately be reconfigured from a controlling ground station to cover the lost area. Further, in the case where an entire satellite is lost due to a malfunction, the configuration of spot beams should be such that another satellite in orbit may be moved to a different longitude and have certain of its feeds set up to take over for the satellite that has malfunctioned.
In accordance with the teachings of the present invention, a method and a computer program are disclosed in which a constellation of satellites is configured. This method and computer program determine a first set of population centers to be covered by a first satellite. The method and computer program then determine a second set of population centers to be covered by a second satellite. Thereafter, the method and computer program determine a third set of population centers which are all common population centers between the first set of population centers and the second set of population centers. Thereafter, mapping of a first union of the first set of population centers and the second set of population centers onto a feed antenna array for the first satellite is done. Finally, the method effects a mapping of a second union of the second set of population centers and the third set of population centers onto a feed antenna array for the second satellite.
Further, in accordance with the present invention. there are provided a method and a computer program for configuring feeds on an antenna of a satellite. This method and computer program determine a first set of primary population centers to be covered by the satellite. The method and computer program then determine a second set of secondary population centers to be covered by the satellite. Thereafter, a mapping occurs of the first set and the second set into the feeds of the antenna of the satellite. Finally, the connectivity is determined between the first set and the second set to maximize at least one optimization criterion.
Further in accordance with the present invention, a method and computer program for configuring several feeds on several satellites are disclosed to supply backup redundancy for a failed satellite. This method and computer program determine a first set of population centers to be covered by a first satellite. The method and computer program then determine a second set of population centers to be covered by a second satellite. Mapping is then done on the first set of population centers onto the feed array of the first satellite. Then, mapping of a second set of population centers onto the feed array of the second satellite is done. Finally, the union between the mapped first set of population centers and the mapped second set of population centers is determined.
Additional objects, features and advantages of the present invention will become apparent from the following description and the appended claims when taken in connection with the accompanying drawings.